The proliferation of new top-level domains (TLDs) has introduced a significant security vulnerability known as domain collision, particularly affecting organizations that have historically used internal domain names in TLDs that were not previously available for public registration. This issue has been exacerbated by the recent liberalization of the .ad TLD, the country-code TLD for Andorra, which was opened to global registration without restrictions in late 2024. Prior to this change, many organizations, particularly those utilizing Microsoft’s Active Directory (AD) for network resource management and user authentication, adopted internal domain names such as “corp.ad” under the assumption that the .ad TLD was restricted and thus safe from external conflicts. However, with the .ad domain now freely available for registration by any entity worldwide, domain hunters—individuals or groups who register domains for speculative or malicious purposes—can easily exploit this situation, leading to severe security risks for affected organizations. This paper examines the domain collision vulnerability in the context of the .ad TLD’s policy shift, explores the specific risks associated with internal domains like “corp.ad,” and discusses the broader implications for organizational cybersecurity.
Background: Active Directory and Internal Domain Usage
Microsoft’s Active Directory is a widely used service that manages network resources, user authentication, and access control within corporate environments. When setting up an Active Directory domain, organizations must choose a domain name that uniquely identifies their internal network. Historically, to avoid conflicts with publicly registered domains, many organizations opted for domain names in TLDs that were either not yet delegated or were restricted to specific geographic or organizational use. The .ad TLD, being the country-code TLD for Andorra, was one such domain that was perceived as safe for internal use due to its previous registration restrictions, which limited ownership to Andorran entities or trademark holders.
For example, an organization might have chosen “corp.ad” as its internal Active Directory domain, assuming that the .ad TLD would not be available for public registration. This practice was common, as it provided a seemingly unique namespace that was unlikely to overlap with external domains. However, the assumption of perpetual restriction has proven faulty with the recent changes in the .ad domain’s registration policy.
The Domain Collision Vulnerability
Domain collision, also known as namespace collision, occurs when an internal domain name used within a private network overlaps with a publicly registered domain name on the global Domain Name System (DNS). This overlap can lead to several security risks:
- Information Leakage: Devices on the internal network may inadvertently send DNS queries for the internal domain to public DNS servers, potentially leaking sensitive information such as usernames, passwords, or internal network configurations.
- Man-in-the-Middle Attacks: If a malicious actor controls the public domain that matches the internal domain, they can intercept traffic intended for the internal network, allowing them to capture credentials or redirect users to malicious sites.
- Unauthorized Access: In some cases, the collision can enable external actors to access internal resources or services that were intended to be private.
The risk is particularly acute for organizations using Microsoft’s Active Directory, as AD relies heavily on DNS for name resolution and service discovery. If an internal AD domain like “corp.ad” is registered publicly by a third party, devices attempting to authenticate or access internal resources may instead connect to the public domain, exposing sensitive data or enabling unauthorized access.
The .ad TLD Policy Change and Its Implications
Prior to 2024, the .ad TLD was restricted to Andorran registrants or trademark holders, with each registration requiring pre-approval. However, in a significant policy shift, the .ad registry liberalized its registration process in two key phases:
- May 22, 2024: The registry began requiring the use of accredited registrars for domain purchases, discontinuing direct registrations from the registry.
- October 22, 2024: The registry opened the .ad TLD to any natural or legal person worldwide, without the need for trademark ownership or local presence, and removed the pre-validation requirement, allowing immediate domain registration.
This policy change has made it possible for anyone, including domain hunters, to register domains like “corp.ad” with minimal barriers. Domain hunters, who often register domains for resale or malicious purposes, can now easily acquire such domains, exploiting the domain collision vulnerability to target organizations that have used these names internally.
Specific Risks Associated with “CompanyName.ad”
The TLD domain “.ad” is particularly problematic because it is a generic and commonly used name for corporate internal networks. Many organizations, especially those that set up their Active Directory environments before the .ad TLD’s liberalization, may have adopted “CompanyName.ad” or similar variants (e.g., “internal.ad,” “hq.ad”) as their internal domain names. With the .ad TLD now open to public registration, multiple organizations could be affected if a single entity registers “CompanyName.ad” and exploits the collision.
The risks include:
- Credential Theft: If internal devices attempt to authenticate against the public “CompanyName.ad” domain, usernames and passwords could be captured by the domain’s controller.
- Traffic Interception: Internal traffic intended for the organization’s private network could be redirected to the public domain, allowing for man-in-the-middle attacks.
- Service Disruption: Organizations may experience disruptions in internal services if DNS queries are resolved incorrectly due to the collision.
Moreover, because the .ad TLD is now globally accessible, the potential for widespread exploitation is significant. Unlike TLDs that are still restricted or have higher barriers to entry, the ease of registering .ad domains increases the likelihood of malicious actors targeting this vulnerability.
Broader Implications for Organizational Cybersecurity
The domain collision issue is not unique to the .ad TLD; it has been a known vulnerability exacerbated by the proliferation of new TLDs. As more TLDs become available for public registration, organizations that have relied on previously undelegated or restricted TLDs for their internal domains face increasing risks. The .ad case serves as a stark example of how changes in TLD registration policies can suddenly expose organizations to security threats that were previously mitigated by restrictive access.
Organizations using internal domains in TLDs that are now publicly available must take immediate action to mitigate these risks. Potential mitigation strategies include:
- Renaming Internal Domains: Organizations can rename their Active Directory domains to use TLDs that are less likely to be registered publicly, such as those reserved for internal use (e.g., .internal).
- Implementing Split DNS: By configuring split DNS, organizations can ensure that internal DNS queries are resolved locally, while external queries are handled by public DNS servers.
- Monitoring and Defensive Registration: Organizations can monitor for registrations of their internal domain names in public TLDs and consider defensively registering these domains to prevent exploitation.
However, these measures can be costly and disruptive, particularly for large organizations with complex network infrastructures. The need for such actions underscores the importance of proactive domain management and the consideration of long-term TLD availability when designing internal network architectures.
Conclusion
The liberalization of the .ad TLD in 2024 has introduced a significant security risk for organizations that have used internal domain names like “corp.ad” in their Active Directory environments. The domain collision vulnerability, once a theoretical concern, has become a pressing issue as domain hunters and malicious actors can now easily register these domains and exploit the resulting namespace conflicts. This situation highlights the broader challenges posed by the expansion of the global domain name system and the need for organizations to adopt more resilient naming conventions and security practices. As the domain landscape continues to evolve, vigilance and adaptability will be essential to safeguarding internal networks from external threats.